1. Field of the Invention
The present invention relates to growth of films of material, and, more particularly, to the growth of diamond-type films and related devices.
2. Description of the Related Art
Diamond is a useful industrial material, providing hard surfaces for cutting tools, coatings for infrared optics, and thermally conductive electrical insulators for electronic devices. Synthetic diamonds have been produced under high-pressure and high-temperature conditions since 1955; and polycrystalline diamond films can be grown at moderate temperatures and pressures. See D. Vitkavage et al, Plasma Enhanced Chemical Vapor Deposition of Polycrystalline Diamond and Diamond-like Films, 6 J. Vac.Sci.Tech. A 1812 (1988). U.S. Pat. Nos. 3,030,187 and 3,030,188 disclose pyrolysis of hydrocarbon gases to deposit diamond despite the thermodynamic preference for graphite formation by including hydrogen gas which preferentially reacts with graphite and removes it. Similarly, diamondlike films, which are amorphous and contain a large fraction of carbon bonds in the sp.sup.2 configuration, can be formed by rf plasma deposition, low-energy ion beam deposition, dc glow discharge deposition, and sputtering. See J. Angus et al, Dense "Diamond-like" Hydrocarbons as Random Covalent Networks, 6 J.Vac.Sci.Tech. A 1778 (1988). However, diamondlike films have inferior hardness for use as cutting tool coatings and have inferior thermal conductivity for use with electronic devices.
The known methods of growth of diamond films on non-diamond substrates have the problem of formation of nucleation sites. The most common substrate preparation procedure includes abrasion with diamond grit. It is believed that small imbedded diamonds act as nucleation sites for the subsequent diamond film growth. But even with diamond-grit-abrasion substrate preparation, grown diamond "films" more closely resemble loose piles of individual diamonds; the nucleation density is apparently too low to readily from a continuous diamond film. This problem is especially severe for those growth conditions that produce the most perfect diamond, as gauged by SEM and Raman spectra. For example, decomposition of a mixture of methane in hydrogen over a hot silicon substrate will yield reasonable diamond quality but have low nucleation density (and high porosity) for low methane concentrations (e.g., 0.5%) but will yield diamondlike films which have poor crystallinity but good surface coverage and low porosity for higher methane concentrations (e.g., 2%).